Gentec 203605, User Manual

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Beamage-M² User Manual Revision 6 40
7.6. THE BEAM DISAPPEARS FROM THE SENSOR
When the beam disappears from the sensor, it must be realigned. The conditions for a good alignment on
the whole carrier travel are:
•
While the carrier is in its farthest position, the beam
must be centred on the Beamage’s sensor.
•
The beam must be centred on the lens.
Make sure your laser does not move relative to the Beamage-M² setup during the experiment.
For more details about the beam alignment, see section 2.2 Laser alignment.
7.7. ACTUAL SETTINGS DO NOT ALLOW AN M
2
MEASUREMENT
Measuring the M
2
of a diverging laser may pull the beam waist position beyond the reach of the system. In
this case, using a lens with a shorter focal length will bring the waist closer to the measured span and
therefore, allow the M
2 measurement.
In case you find Z0 to be out of the range or ZR to be too high, you will need to change the lens. Here is
the procedure to replace a lens. Different cases of bad focal length choice are presented right after.
1. Replacing the lens:
a. Lower all the ND filters.
b. Unscrew the iris and the iris adapter.
c. Unscrew the lens tube and put it in a clean plastic bag.
d. Take the lens you need from the transport case and screw it in place of the one you just
took away.
e. Screw the iris and the adapter in front of the new lens.
7.8. LENS CHOOSING GUIDE
Here is a quick guide to help you choose a suitable lens.
In case you get:
1. Z0 < 186 mm
a. The focal length is too short, change for a longer focal length.
2. Z0 > 580 mm
a. The focal length is too long, change for a shorter focal length.
3. ZR > 100 mm
a. The Rayleigh length is too long to return an ISO M² value.
b. This means the divergence is too low.
c. Change the lens for a shorter focal length to raise divergence.
4. ZR > 58 mm
a. The Rayleigh length is too long to return a Gentec approved commercial
M² measurement (7 ZR must fit within
the stage’s range).
b. This means the divergence is too low.
c. Change the lens for a shorter focal length to increase the divergence.